Conventional modular vehicle window panels consist of at least one panel of glass shaped to generally fit in an opening defined by the sheet metal of the vehicle and sealed therein by a gasket attached to the peripheral edge of the glass panel. Traditionally, the gasket was formed such that the gasket completely enclosed the peripheral edge of the panel and included flanges which extended inwardly on opposing surfaces of the panel. This "three-sided encapsulation" provided mechanical anchoring of the gasket to the panel.
Contemporary modular vehicle window panels may have a gasket formed on at least one surface of the panel along the peripheral edge of the panel but do not have gasket material extending onto the exterior surface. Such gaskets are formed along the inner surface of the panel proximate the peripheral edge and are known in the art as single-sided encapsulation. Other shapes or forms of gaskets include a portion which wraps partially around and onto the peripheral edge but does not extend onto the exterior surface and are known in the art as two-sided encapsulation. The two-sided encapsulant gasket along the peripheral edge can be flush with the exterior surface of the panel. Single-sided or two-sided gasketed panels have been sometimes designated "flush glazings or panels" because of the absence of gasketing material extending onto the exterior surface of the panel and because of their ability to facilitate mounting of window glazings generally flush with the exterior of the sheet metal body of the vehicle.
A problem with single- or two-sided encapsulant glazings or panels is that they do not offer the mechanical retention of the window offered by "three-sided encapsulant" modular windows. In the case of single- or two-sided gasketed panels, the gasket may be bonded to the sheet metal or the glass panel may be bonded to the sheet metal to retain the glass in the window opening such as by use of an adhesive. Mechanical fasteners have also been used to retain the modular panel in the window opening. An example of one specific mechanical fastener includes a stud partially encapsulated by the gasket material located about or near the peripheral edge of the panel. The stud may have a head spaced from the panel and encapsulated in the gasket material such that the stud floats with respect to the panel. The stud also includes a shaft which extends through the sheet metal of the window opening and is secured such as by a nut to retain the panel in the vehicle. Although a stud is one type of fastener used, others may also be used including clips and ratcheted studs or trees.
In terms of selection of gasketing material, prior artisans have used a variety of melt-processible materials for window encapsulation, with injection molding of plasticized polyvinylchloride (PVC) resin enjoying commercial success, particularly for three-sided encapsulation, and have used materials, principally thermosetting urethanes, that are not melt processible, but are rather formed by liquid injection molding such as in reaction injection molding (RIM) of polyurethane. Melt processing is a desirable technique for fabrication of the gaskets of this invention for a variety of reasons. For example, melt processing involves processing at elevated temperature, such as in excess of 100.degree. C., and is amenable to formation of gaskets onto substrates that are themselves heated. Such elevated temperature is useful for enhancing adhesion between the gasket and the window panel. Also, unlike RIM of thermosetting urethane, melt processing allows potential use of a wide variety of materials, both thermoplastic and thermosetting, with the added advantage of allowing formation using melt processing of recyclable gaskets that are desired to assist preservation of the environment.
However, although in the past a wide variety of melt-processible materials, such as PVC, have been suggested for forming gaskets such as single- or two-sided gaskets, particular attention has not been paid to the long-term bonding characteristic of the gasket to the glass when the assembly is attached to the vehicle by mechanical fasteners floating in the gasket material. Loads imposed on the fasteners embedded in the gasket are transferred to the bond line between the panel and the gasket. The types of loads include tensional-loads or off-form loads caused by differences or variations in the shape of the window panel and the sheet metal opening; static loads on the panel assembly itself caused by the weight of the glazing on the fasteners; and dynamic loads imposed on the studs through normal use, including vibration of the vehicle, acceleration/deceleration of the vehicle, wind and air pressure on the interior and exterior of the vehicle, and other activities such as the opening and closing of the vehicle doors.
In single- and two-sided encapsulations such as those described above, it has been found that over time, the bond between the panel and the gasket may fail in adhesion in an area localized about the fastener. Such failure can result in water leaks, wind noise, and rattling of the window panel in the vehicle opening. Previous solutions to these problems include directly attaching the fastener to the glass panel so that the loads are transferred directly to the window panel instead of to the gasket, or even dispensing with fasteners and utilizing direct gasket-to-vehicle adhesion using an adhesive applied substantially between the gasket and vehicle opening. Such attachment methods result in extra processing and may be time-consuming resulting in additional costs in the panel. Other solutions include closer stamping tolerances and fabrication of the welding of the window opening, which also may result in increased time and labor expenditures resulting in a more expensive product. Additional solutions include use of non-melt-processible gasketing material such as RIM of thermosetting urethane with the consequent loss of the benefit associated with melt processing described above.